typedef PK_ERROR_code_t (*PK_MARK_open_f_t)(PK_MARK_t, PK_LOGICAL_t);
typedef PK_ERROR_code_t (*PK_MARK_close_f_t)(PK_MARK_t);
typedef PK_ERROR_code_t (*PK_MARK_write_f_t)(PK_MARK_t, int, const char*);
typedef PK_ERROR_code_t (*PK_MARK_read_f_t)(PK_MARK_t, int, char*);
typedef PK_ERROR_code_t (*PK_MARK_check_f_t)(PK_MARK_t, PK_LOGICAL_t *);
typedef PK_ERROR_code_t (*PK_MARK_delete_f_t)(PK_MARK_t);

struct PK_MARK_frustrum_s
    {
    PK_MARK_open_f_t   open_fn;     --- open a rollmark for read or write
    PK_MARK_close_f_t  close_fn;    --- close a rollmark
    PK_MARK_write_f_t  write_fn;    --- write data to a rollmark
    PK_MARK_read_f_t   read_fn;     --- read data from a rollmark
    PK_MARK_check_f_t  check_fn;    --- check if mark is still valid
    PK_MARK_delete_f_t delete_fn;   --- delete a rollmark
    };
typedef struct PK_MARK_frustrum_s PK_MARK_frustrum_t;




This data structure holds pointers to six rollmark functions that the
application wishes to register with the PK using PK_MARK_start.